Lactation — Core Principles

Core Principles

Lactation is the process of milk production and secretion from the mammary glands in mammals, essential for nourishing the newborn. It commences after childbirth, following the expulsion of the placenta, which causes a sharp decline in inhibitory hormones like estrogen and progesterone.

The primary hormone for milk synthesis is prolactin, secreted by the anterior pituitary, which stimulates alveolar cells to produce milk components. Milk ejection, or the 'let-down reflex,' is mediated by oxytocin, released from the posterior pituitary in response to suckling.

Oxytocin causes myoepithelial cells around the alveoli to contract, pushing milk into the ducts. The first milk, colostrum, is rich in antibodies, providing crucial immunity. Mature milk provides balanced nutrition.

This entire process is a neuro-hormonal reflex, maintained by a positive feedback loop where suckling ensures continued milk supply.

Important Differences

vs Colostrum vs. Mature Milk

Aspect	This Topic	Colostrum vs. Mature Milk
Appearance	Thick, yellowish, sometimes clear	Thinner, whiter, more watery
Production Time	First 2-5 days postpartum	From about 2 weeks postpartum onwards
Volume	Small quantities (e.g., 2-20 ml per feed)	Larger quantities (e.g., 60-120 ml per feed and increasing)
Protein Content	High (especially immunoglobulins)	Lower than colostrum, but sufficient for growth
Fat Content	Lower	Higher, providing more calories
Lactose Content	Lower	Higher, providing energy
Immunological Factors	Very high (rich in IgA, lactoferrin, leukocytes)	Present, but in lower concentrations than colostrum
Primary Function	Provides passive immunity, gut maturation, mild laxative effect	Primary source of nutrition for growth and development

Colostrum, the 'first milk,' is a highly concentrated, antibody-rich fluid produced immediately after birth, crucial for providing passive immunity and preparing the newborn's digestive system. It is lower in fat and lactose but packed with protective proteins. In contrast, mature milk, produced later, is a more voluminous, calorically dense fluid, higher in fat and lactose, designed to meet the growing infant's nutritional demands for sustained growth and development, while still offering some immunological benefits.